ImportanceSARS-CoV-2, which causes COVID-19, poses considerable morbidity and mortality risks. Studies using data collected during routine clinical practice can supplement randomized clinical trials to provide needed evidence, especially during a global pandemic, and can yield markedly larger sample sizes to assess outcomes for important patient subgroups.ObjectiveTo evaluate the association of remdesivir treatment with inpatient mortality among patients with COVID-19 outside of the clinical trial setting.Design, Setting, and ParticipantsA retrospective cohort study in US hospitals using health insurance claims data linked to hospital chargemaster data from December 1, 2018, to May 3, 2021, was conducted among 24 856 adults hospitalized between May 1, 2020, and May 3, 2021, with newly diagnosed COVID-19 who received remdesivir and 24 856 propensity score–matched control patients.ExposureRemdesivir treatment.Main Outcomes and MeasuresAll-cause inpatient mortality within 28 days of the start of remdesivir treatment for the remdesivir-exposed group or the matched index date for the control group.ResultsA total of 24 856 remdesivir-exposed patients (12 596 men [50.7%]; mean [SD] age, 66.8 [15.4] years) and 24 856 propensity score–matched control patients (12 621 men [50.8%]; mean [SD] age, 66.8 [15.4] years) were included in the study. Median follow-up was 6 days (IQR, 4-11 days) in the remdesivir group and 5 days (IQR, 2-10 days) in the control group. There were 3557 mortality events (14.3%) in the remdesivir group and 3775 mortality events (15.2%) in the control group. The 28-day mortality rate was 0.5 per person-month in the remdesivir group and 0.6 per person-month in the control group. Remdesivir treatment was associated with a statistically significant 17% reduction in inpatient mortality among patients hospitalized with COVID-19 compared with propensity score–matched control patients (hazard ratio, 0.83 [95% CI, 0.79-0.87]).Conclusions and RelevanceIn this retrospective cohort study using health insurance claims and hospital chargemaster data, remdesivir treatment was associated with a significantly reduced inpatient mortality overall among patients hospitalized with COVID-19. Results of this analysis using data collected during routine clinical practice and state-of-the-art methods complement results from randomized clinical trials. Future areas of research include assessing the association of remdesivir treatment with inpatient mortality during the circulation of different variants and relative to time from symptom onset.